Amalgam restorations are subjected to a variety of mechanical forces and corrosion phenomena which are believedto contribute to deterioration. Yet, much more information is needed to define the nature of changes that occur with the various amalgam types in clinical service. This program consists of taking a large number of well characterized amalgam restorations which have been removed and analyzing their microstructural characteristics. The microstructures will then be compared to the clinical characteristics of the restorations in order to define what microstructural changes contributed to the observed clinical status. The amalgam restorations will be retrieved from the 2,700 amalgam restorations that have been undergoing detailed clinical evaluation over the past 8 years by the Dutch Amalgam Group. These restorations are representative of amalgam alloys covering the spectrum of available amalgams and have been clinically evaluated at regular intervals since placement. From estimates of failure and replacement rates in this population, approximately 100 restorations will be available yearly for microstructural analysis. Fifty of the most representative restorations will be analyzed each year. Microstructural analysis will be carried out by scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS). Attention will be given to changes in phase content, corrosion phenomenon, and evidence of mechanical deformation. These changes will be correlatedwith clinical rating and amalgam type. Where necessary, x-ray diffraction (XRD) will be used for definitive phase identifications. Finally, these results will be correlated with residual mercury contents and microhardness values to provide further comparisons with standard specimens and data. The major disciplines involved in this work are: restorative dentistry and materials science.